The dtb= parameter is no longer the primary mechanism for providing a
devicetree to the kernel. Now either firmware or the boot selector (ex.
Grub) should provide the devicetree and dtb= should only be used for
debug or when using firmware that doesn't understand DT.
Update the EFI stub documentation to reflect the current usage.
Signed-off-by: Grant Likely <[email protected]>
Reviewed-by: Alexander Graf <[email protected]>
Acked-by: Leif Lindholm <[email protected]>
Acked-by: Olof Johansson <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Jonathan Corbet <[email protected]>
---
Resending because original post included Arm corporate disclaimer.
Documentation/efi-stub.txt | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/Documentation/efi-stub.txt b/Documentation/efi-stub.txt
index 41df801f9a50..833edb0d0bc4 100644
--- a/Documentation/efi-stub.txt
+++ b/Documentation/efi-stub.txt
@@ -83,7 +83,18 @@ is passed to bzImage.efi.
The "dtb=" option
-----------------
-For the ARM and arm64 architectures, we also need to be able to provide a
-device tree to the kernel. This is done with the "dtb=" command line option,
-and is processed in the same manner as the "initrd=" option that is
+For the ARM and arm64 architectures, a device tree must be provided to
+the kernel. Normally firmware shall supply the device tree via the
+EFI CONFIGURATION TABLE. However, the "dtb=" command line option can
+be used to override the firmware supplied device tree, or to supply
+one when firmware is unable to.
+
+Please note: Firmware adds runtime configuration information to the
+device tree before booting the kernel. If dtb= is used to override
+the device tree, then any runtime data provided by firmware will be
+lost. The dtb= option should only be used either as a debug tool, or
+as a last resort when a device tree is not provided in the EFI
+CONFIGURATION TABLE.
+
+"dtb=" is processed in the same manner as the "initrd=" option that is
described above.
--
2.11.0
On 6 September 2018 at 20:29, Grant Likely <[email protected]> wrote:
> The dtb= parameter is no longer the primary mechanism for providing a
> devicetree to the kernel. Now either firmware or the boot selector (ex.
> Grub) should provide the devicetree and dtb= should only be used for
> debug or when using firmware that doesn't understand DT.
> Update the EFI stub documentation to reflect the current usage.
>
> Signed-off-by: Grant Likely <[email protected]>
> Reviewed-by: Alexander Graf <[email protected]>
> Acked-by: Leif Lindholm <[email protected]>
> Acked-by: Olof Johansson <[email protected]>
> Cc: Ard Biesheuvel <[email protected]>
> Cc: Jonathan Corbet <[email protected]>
Acked-by: Ard Biesheuvel <[email protected]>
> ---
>
> Resending because original post included Arm corporate disclaimer.
>
> Documentation/efi-stub.txt | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/efi-stub.txt b/Documentation/efi-stub.txt
> index 41df801f9a50..833edb0d0bc4 100644
> --- a/Documentation/efi-stub.txt
> +++ b/Documentation/efi-stub.txt
> @@ -83,7 +83,18 @@ is passed to bzImage.efi.
> The "dtb=" option
> -----------------
>
> -For the ARM and arm64 architectures, we also need to be able to provide a
> -device tree to the kernel. This is done with the "dtb=" command line option,
> -and is processed in the same manner as the "initrd=" option that is
> +For the ARM and arm64 architectures, a device tree must be provided to
> +the kernel. Normally firmware shall supply the device tree via the
> +EFI CONFIGURATION TABLE. However, the "dtb=" command line option can
> +be used to override the firmware supplied device tree, or to supply
> +one when firmware is unable to.
> +
> +Please note: Firmware adds runtime configuration information to the
> +device tree before booting the kernel. If dtb= is used to override
> +the device tree, then any runtime data provided by firmware will be
> +lost. The dtb= option should only be used either as a debug tool, or
> +as a last resort when a device tree is not provided in the EFI
> +CONFIGURATION TABLE.
> +
> +"dtb=" is processed in the same manner as the "initrd=" option that is
> described above.
> --
> 2.11.0
>
On Thu, 6 Sep 2018 19:29:27 +0100
Grant Likely <[email protected]> wrote:
> The dtb= parameter is no longer the primary mechanism for providing a
> devicetree to the kernel. Now either firmware or the boot selector (ex.
> Grub) should provide the devicetree and dtb= should only be used for
> debug or when using firmware that doesn't understand DT.
> Update the EFI stub documentation to reflect the current usage.
>
> Signed-off-by: Grant Likely <[email protected]>
> Reviewed-by: Alexander Graf <[email protected]>
> Acked-by: Leif Lindholm <[email protected]>
> Acked-by: Olof Johansson <[email protected]>
> Cc: Ard Biesheuvel <[email protected]>
Applied, thanks.
jon